In many load-lifting mechanisms and systems, the lifting rope is expected to possess a combination of physically contradictory properties such as high flexibility and wear resistance. The former is attained through the use of a large number of thin wires while the latter calls for a small number of thick wires. Therefore, none of the prior art ropes are known to possess a combination of the foregoing properties.
Known in the art is a great number of structural varieties of flattened strand ropes and cables whose strands consist of round wires wound on a core (cf., German Patent No. 567,004, F.R.G. Patent No. 830,015, U.S. Pat. Nos. 2,018,461 and 3,457,718, U.S.S.R. Inventor's Certificates Nos. 89,792 and 500,305, etc.) or of non-round shaped wires wound on a core (cf., German Patent No. 656,123, U.S. Pat. No. 2,122,911, etc.).
While featuring an increased wear resistance, prior art flattened strand ropes have a high flexural rigidity. Because of this reason, they are mostly used in mines, lifting mechanisms and other systems utilizing pulley blocks and drums of large diameter. Attempts at using such ropes in lifting mechanisms having pulleys and drums of relatively small diameters revealed their inadequacy due to low efficiency. This can be attributed, mainly, to the fact that the flattened strand ropes, especially those of large diameters, require relatively thick and, consequently, less flexible wires (in comparison with the underlying layer wires) for forming the outer layer of strands. Moreover, large-size wires manufactured in the conventional manner have a lower ultimate strength than thin ones, which results in a lower summary tensile strength of the rope.
Wires in ropes of the former structural group, due to their round profile, are in contact with the adjacent wires in the layer over helical lines, thus leaving the strands with considerable spaces free of metal. Wires in the rope strands in the former structural group are subject to rapid wear. The tensile strength of the ropes as such is limited by a relatively low degree of filling the cross-sectional area of the strands with metal and by a relatively low strength of the wires due to the large size of the diameter.
The shaped profile of wires in ropes of the latter structural group makes for the contact of adjacent wires over helical surfaces, a high degree of wear resistance and a high degree of filling the strand cross-sectional area with metal and, at the same time, it results in a lower flexibility and the lowest possible wire strength, all other things equal, inasmuch as thick wires are required for making up rope strands of the latter structural group.
Therefore, prior art flattened strand rope structures fail to ensure the combination of high flexibility, wear resistance and strength in a single rope.